Method of preparing thiiranes from mercaptoalcohols

ABSTRACT

The method comprises continuously adding mercaptoalcohols to a heated solution of a dehydration catalyst dissolved in a liquid diluent. The diluent and catalyst are of low volatility at the reaction temperature. The thiirane is continuously removed from the reaction mixture.

United States Patent Jon E. Fletcher;

Rodney A. Nelson, both of Midland, Mich. 759,775

Sept. 13, 1968 Nov. 23, 1971 The Dow Chemical Company Midland, Mlch.

Inventors Appl. No. Filed Patented Assignee METHOD OF PREPARINGTHIIRANES FROM [56] References Cited UNITED STATES PATENTS 2,436,2332/1948 Signaigo 260/327 OTHER REFERENCES Adkins, Reactions of Hydrogen,(U. Wisconsin, Madison, 1937), PP- 25- 26.

Primary Examiner-Henry R. .liles Assistant Examiner-Cecilia M. ShurkoAttorneys-Griswold and Burdick and S. Hoynak ABSTRACT: The methodcomprises continuously adding mercaptoalcohols to a heated solution of adehydration catalyst dissolved in a liquid diluent. The diluent andcatalyst are of low volatility at the reaction temperature. The thiiraneis continuously removed from the reaction mixture METHOD OF PREPARINGTHIIRANES FROM MERCAPTOALCOHOLS This invention relates to a method ofpreparing thiiranes by dehydrating mercaptoalcohols and moreparticularly pertains to a method of making thiiranes by continuouslyfeeding a mercaptoalcohol to a heated mixture of a dehydrating catalystdissolved in a diluent of low volatility, at a temperature sufficientlyhigh to continuously volatilize the thiirane but under conditions suchthat the diluent or solvent and catalyst are not removed by evaporationand at which the solvent is not decomposed appreciably.

In accordance with this invention compounds of the structure RI! meagre0113' wherein R represents hydrogen, halogen, alkyl, haloalkyl,cycloalky], olefin, alkoxy, aryloxy, aryl, aralkyl, alkaryl, carboxy,hydroxyl, thioalkyl, and thiol groups in which the organic radical hasfrom one to about 10 carbon atoms and R and R" each represents hydrogenand alkyl groups of from one to two carbon atoms and n is a member fromzero to two can be prepared by continuously commingling amercaptoalcohol of the structure where R, R, and R" and n each have thedesignation given above and X and Y each represents -H and -SH and whenone of X and Y is -OH the other is -SH with a mixture consistingessentially of a dehydration catalyst dissolved in a high boilingdiluent, at a temperature such that the thiirane formed is continuouslyremoved by volatilization, but at which the catalyst and its solvent arerelatively nonvolatile.

The thiiranes, which are also termed episulfides or alkylene sulfides,made by the process of this invention are useful for preparinghomopolymers and copolymers by opening of the thiirane ring sulfur atom.The polymers are useful for making films and other articles which arerubbery or plastic in their physical features. The homopolymers andcopolymers can be plastics or elastomers. These can be formed into filmsor sheets, which are useful as protective or coating materials forcellulosic materials, including wood. The polymers can also be molded orextruded into a variety of articles such as containers or tubing. Lowmolecular weight polymers and copolymers are liquids which can be usedas lubricants. The

thiiranes can be used as ingredients in the synthesis of thioethers,which can be oxidized to sulfoxides and sulfones. The oxidized productsare useful as solvents, if liquid and as detergents, if solid.

No method prior to this invention was known for preparing thiiranesdirectly from mercaptoalcohols in good yields, because of the reactivityof the thiirane sulfur atom, especially through polymerization byopening the thiirane ring. The polymerization reaction is especiallysensitive to acid and alkaline catalysis.

Prior art methods describe procedures for obtaining yield of percent ofCH CHCH SH by refluxing 2, 3-dimercaptol-propanol at about ll 1 C. undera vacuum of 10 mm. Hg, while fractionating the thiirane from themixture. The catalysts described include zinc chloride, ferric chloride,HCl HBr and a mineral acid. No solvent was used.

In another process 2,3-dimercapto-l-propanol is dehydrated using abisulfate as a dehydration catalyst. The mercaptopropanol is mixed withfinely divided KHSO, and then the mixture is heated to l03-105 C. undera vacuum of 3 mm. Hg. Nitrogen is used to sweep out the thiirane as itforms. A yield of 69.5 percent of CH CHCHgSH is reported for thisprocess. When mercaptoethanol was substituted for2,3-dimercapto-1-propanol, a yield of 5.4 to 12.1 percent is obtained,depending on the conditions and techniques used for dehydration andrecovery of the ethylene sulfide.

in contrast, the procedure of this invention consistently producesyields of 78-98 percent of ethylene sulfide.

Representative mercaptoalcohols that can be converted to thiiranesinclude those of the generic formula where one of X and Y is -OH and theother -SH, R and R" can be H, -CH or -C l-l,, and R can be H, Ci-l Cl,CH Br, CH F, CH =CH, Br, Cl, F, OH, SH, CH -0, C,H,O-, C H O-, C H O-,allyloxy, allylthio, phenyl, phenoxy, halophenyl, halophenoxy, and alkylring-substituted derivatives of the phenyl compounds. As mentionedabove, R can be any organic group having one to 10 carbon atoms which isnot reactive with the ring sulfur atom of the thiirane that is formed.It is necessary that the thiirane be sufficiently volatile at thereaction temperature to be readily removed as a vapor.

The reaction is carried out at elevated temperatures of ll0-200 C. andpreferably from about l25-l65 C. It is to be understood that thereaction temperature will necessarily be at least as high as the boilingpoint of the thiirane that is formed under the pressure conditionsemployed. It is preferred to use a reaction temperature which strips thethiirane from the solvent substantially as rapidly as it forms.

The reaction should be carried out under reduced pressure of 1-200 mm.Hg. The preferred range will depend in part on the temperature employedand in part on the boiling point of the solvent and that of the.thiirane. Generally, a preferred pressure range is from 5-100 mm. Hg.It is to be understood that the optimum vacuum for operating the processwill vary somewhat depending on other conditions employed.

The solvents to be used are compounds of high boiling point having avapor pressure no greater than about 10 mm. Hg at C. and which arecapable of dissolving an acidic dehydration catalyst to the extent of atleast 0.1 percent by weight based on the weight of solvent or diluentused, and which do not decompose the diluent appreciably at the reactiontemperature used.

One method for testing the suitability of the diluent or solvent for thepurposes of this invention is to mix l00 parts of the diluent with 0.002to 0.2 acid equivalents or more of the catalyst and titrate an aliquotof the diluent or solvent for the amount of catalyst dissolved. Thesolubility of the mercaptoalcohol can be tested similarly by mixing withthe diluent and analyzing an aliquot for mercaptan groups or sulfur.

If an adequate amount of catalyst is dissolved the solution should beheated to ll0-200 C. under a vacuum of l-200 mm. Hg to estimate thedegree of decomposition of the diluent under these conditions. Usuallydecomposition of the diluent is evidenced by a darkening or evencharring of the diluent. Weight loss and gas evolution are also usefulfor determining degree or decomposition. it is to be understood that adiluent which reacts with the acid catalyst without evidence ofdecomposition can be employed. Typical compounds which can react withl-i SO are alkanols, polyglycols or their monoethers, which form sulfatederivatives.

Representative high boiling solvents or diluents include, but are notlimited to, polyethylene or polypropylene or polybutylene glycols,copolymers of ethylene, propylene or butylene oxides, all of which mustbe liquid at reaction temperature, ethylene or propylene or butyleneglycol monophenyl ethers, the monoor dimethyl, ethyl, propyl or butylethers of diethylene glycol dipropylene glycol or dibutylene glycol, themonoand dimethyl, ethyl, propyl and butyl ethers of triethylene glycol,tripropylene glycol or tributylene glycol, monoand dimethyl, ethyl,propyl and butyl ethers of tetraethylene glycol, tetrapropylene glycol,tetrabutylene glycol, and long chain alkanols having 12 to 20 atoms. Thepolyglycol monoand diethers can be copolymers of two or more of ethylenepropylene and/or butylene oxides.

The range of solvent can be as low as 50 percent and as high as 97-99percent by weight of the reaction mixture.

The dehydration catalysts which can be employed are H 80 H PO,, alcoholsulfates, alcohol sulfonates of two to 20 C atoms, preferably two to 14C atoms, phenyl sulfonic acid, ring alkylated, or halogen substitutedphenyl sulfonic acids, such as tolyl sulfonic acid, chlorophenylsulfonic acid, or ethylphenyl sulfonic acid.

The proportion of catalyst can range from about 0.002 to about 0.2 acidequivalents per 100 parts by weight of solvent. Usually 0.005 to 0.06acid equivalents per 100 parts by weight of solvent is ample and the useof more than about 0.06 acid equivalents of catalyst does not appear toaffect the rate of dehydration any more favorably than that at about the0.06 acid equivalent level.

Addition of a thiirane stabilizer to the reactor is desirable, but notessential. ,The preferred stabilizers are long chain alkyl mercaptansrepresentatives of which are lauryl mercaptan, noctyl mercaptan andt-dodecyl mercaptan. The amount of stabilizer can range from about toabout percent by weight based on the weight of solvent employed.

If desired an inert gas such as CO,,, nitrogen, argon, krypton, xenon,or helium, or water vapor, lower alkanols oran inert organic volatilehydrocarbon such as the lower alkanes having one to about eight carbonatoms or any volatile compound which is nonreactive with the thiiranecan be used as a sweep gas either intermittently or continuously duringthe reaction.

One way of carrying out the process of this invention is to add to thereactor solvent, catalyst and thiirane stabilizer, if used, and heat themixture to the desired temperature and adjust the pressure in thesystem. The mercaptoalcohol, additional solvent and makeup catalyst, ifdesired, with or without the stabilizer and an inert ingredient which isa vapor at the temperature and pressure employed, if desired, are fedinto the reactor. The thiirane which forms together with water andusually small amounts of unreacted mercaptoalcohol are flashed from thesolvent. The vapors which are removed from the reaction system can beseparated and purified by distillation. A distillation column can beplaced at the top of the reactor, if desired, or it can be employed as aseparate unit in the process train. If the distillation column is at thetop of the reactor the small amount of unconverted mercaptoalcohol canbe condensed preferentially and returned to the reactor. Small amountsof solvent are withdrawn from the reactor to keep the level of solventsubstantially uniform.

The examples which follow are intended to illustrate the invention, butnot to limit it. All parts are by weight unless otherwise specificallyindicated.

EXAMPLE 1 The reactor consisted of a l-liter round bottomed flask fittedwith a stirrer and a fractionating column which had a reflux head and aninlet for a solution of mercaptoalcohol and make up H 50 dissolved in asolvent. The column was connected to a condenser and a cold trap cooledwith dry ice. The condenser was cooled with a CaCl -Water mixture havinga temperature of -10 to l5 C. or water at a temperature of about 4 C.

The cold trap was connected to a vacuum pump.

The base of the reactor contained a valve through which solvent mixturecould be withdrawn at a rate such that the liquid level in the flaskcould be maintained substantially constant.

The reactor was charged with 650 parts of a technical grade oftriethylene glycol monobutyl ether which contains some higher polymerichomologues, as a solvent, 20 parts of tdodecyl mercaptan and 4.9 partsof 95 percent H 50 A vacuum of 40 mm. Hg was drawn on the system and themixture was heated to 145 C. and held at approximately this temperatureduring the entire run. A feed consisting of 78 percent2-mercaptoethanol, 19.9 percent of the solvent mentioned above, 1.6percent water and 0.5 percent H 80 was added to the reactor continuouslyat a rate of about 3 ml. per minute until a total of 1,164 g. werecharged. A solvent stream was continuously removed from the reactor tomaintain the liquid level substantially constant. Of the 908 grams of2-mercaptoethanol fed, 121 grams were recovered from the overhead waterlayer and 559 grams of ethylene sulfide were formed. This represents ayield of 92.3 percent on the mercaptoethanol reacted and 81.4 percent onthe mercaptoethanol fed. The water layer and the solvent which had beenwithdrawn from the reactor can be filtered and recycled to the process.

EXAMPLE 2 The apparatus used in this example was the same as thatdescribed above. The reactor was charged with 650 parts of a technicalgrade of triethylene glycol monobutyl ether, 19.5 parts of t-dodecylmercaptan and 5.2 parts of percent H 80 A vacuum of 73 mm. Hg was drawnon the system and the mixture was heated to 144 C. Then 2,520 parts of amixture consisting of 49.4 weight percent of mercapto-2- propanol, 10.9percent water, 1.6 percent t-dodecyl mercaptan, 37.8 percent technicalgrade triethyleneglycol monobutyl ether and 0.3 percent H 50 were addedto the reactor continuously at a rate of about 10 ml. per minute, whilemaintaining the temperature at about C. Solvent was continuously removedto maintain the liquid level in the reactor substantially constant. Thepropylene sulfide water and unconverted mercapto propanol were removedcontinuously. The solvent can be filtered and recycled.

The overhead contained 883 parts of propylene sulfide and 92 parts ofunconverted mercaptopropanol. The yield of thiirane on themercaptopropanol reacted was 96.1 percent and that on themercaptopropanol charged was 88.9 percent.

EXAMPLE 3 In this run the reactor was connected by a side arm to afractionating column fitted with a reflux head. The column had areboiler of l-liter capacity. The overhead from the fractionating columnpassed through a condenser cooled with a liquid having a temperature of0 to l0 C. The receiver was cooled with solid C0,. The vapors from thecondenser passed through a cold trap cooled with solid CO-,

The reactor was charged with 700 parts of polyethylene glycol having amolecular weight of about 400 and 5.25 parts of 95 percent H 80 Thereboiler was charged with 500 ml. of distilled water and 7 grams ofmonosodium phosphate monohydrate. A vacuum of 78 mm. Hg was drawn on thesystem and the mixture in the reactor was heated to 143 C. Then 2,820parts of a feed consisting of 48.2 percent l-mercapto-2-propanol, 0.2percent H 80 25.5 percent water and 26.1 percent of the above definedpolyethylene glycol at a rate of about ml. per minute were added, whilemaintaining the temperature at about 143 C. The reactor pressure variedbetween 75 and 85 mm. Hg, averaging about 80 mm.

Propylene sulfide, water and unconverted mercaptopropanol were flashedinto the continuous still. Of the 1,360 parts of mercaptopropanolcharged 480 parts were unconvetted. Also 602 parts of propylene sulfidewere recovered. The yield on the mercapto alcohol reacted was 85.0percent.

EXAMPLE 4 The apparatus of example 1 was used for this run.

The reactor was charged with 650 parts of a technical grade oftriethylene glycol monobutyl ether, parts of t-dodecyl mercaptan, and4.9 parts of 95 percent H SO A vacuum of a. 65 mm. Hg was'drawn on thesystem and the temperature in the reactor was raised to 145 C. Then 707parts of a feed consisting of 5.85 percent l-mercapto-Z-propanol and94.15 percent of 1-mercapto-2-butanol were continuously charged to thereactor at a rate of about 3 ml. per minute.

The organic layer from the distillation totaled 521 grams. This wasfractionated and found to contain 27.5 parts propylene sulfide, 466.5parts of butylene sulfide and 27 parts of unidentified still bottoms.The yield of thiiranes on the mercaptoalcohols fed was 84.3 percent.

EXAMPLE 5 The apparatus used in this run was that described in examplel.

The reactor was charged with 600 parts of tripropylene glycol methylether and 3 parts of 95 percent H 80 A vacuum of 68 mm. Hg was drawn onthe system and the reactor contents were heated to 145 C. Then 2,480parts of feed consisting of 63 percent 1-mercapto-2-propanol, 1.62percent isopropanol, .65 percent bis-hydroxypropyl sulfide, 12.82percent water, 21.78 percent tripropylene glycol methyl ether and 0.12percent, 95 percent H 50 were added continuously at a rate of about 5ml. per minute. Solvent was withdrawn from the reactor to maintain asubstantially constant liquid level.

The effluent from the still contained 42. 1 parts of unreactedmercaptopropanol and 1,189 parts of propylene sulfide. This is a 97.3percent yield based on the mercaptopropanol converted.

EXAMPLE 6 The apparatus described in example 3 was employed. The flaskwas charged with 675 grams of triethylene glycol monobutyl ethercontaining 0.76 weight percent of H 80, and 3 percent dodecyl mercaptan.A feed mixture containing 49.4 percent l-mercapto-Z-propanol, 10.92percent water, 37.6 percent of the above solvent, containing 715 percentH 50, and a small amount of dodecyl mercaptan was fed at a rate of 655grams per hour. The reaction was run at a pressure of 73 mm. Hg and 144C. During the run of 230 minutes, 93 percent of the mercaptopropanol wasconverted and the yield of propylene sulfide based on the convertedmercapto propanol was 95 percent.

EXAMPLE 7 The reactor of example 3 was charged with 675 grams oftriethylene glycol monomethyl ether containing 0.715 weight percent H80, and 3 percent dodecyl mercaptan. The mixture was heated to 145 C.and a vacuum of 75 mm. Hg was drawn. 1-mercapto-2-propanol withoutsolvent was fed at a rate of 294 g. per hour. During the run of 225minutes, 86 percent of the mercaptoalcohol was reacted and the yield ofpropylene sulfide based on the reacted mercaptoalcohol was 95.5 percent.

EXAMPLE 8 The apparatus described in the previous example was used. Amixture of 675 grams of triethylene glycol monomethyl ether containing0.73 weight percent H 50, and 3.0 percent dodecyl mercaptan was heatedto 145 C. and a vacuum of 40 mm. Hg was drawn on the system. A feedcontaining 78 weight percent mercaptoethanol, 2 percent dodecylmercaptan and 20 percent of the said solvent was fed at a rate of 228 g.per hour over a 370 minute period. in this run 87 percent of themercaptoethanol reacted and the yield of ethylene sulfide based on thereacted mercaptoethanol was 92.3 percent.

EXAMPLE 9 In this run the reactor was the same as described inexample 1. The reactor was charged with 250 g. of diethylene glycolmonobutyl ether containing 0.75 weight percent H The mixture was heatedto 140 C. and a vacuum of 75 mm. Hg was drawn. A total of 500 g. ofl-mercapto-Z-propanol at a rate of 2.75 g. per minute was fed into thereactor at the conditions described. During the run about 92 percent ofthe mercaptopropanol was converted and the yield of propylene sulfidebased on the converted mercaptoalcohol was 95 percent.

When mercaptoethanol was substituted for mercaptopropanol under the samereaction conditions and feed rates, the conversion of themercaptoethanol was 92 percent, with a yield of 92 percent ethylenesulfide based on the converted mercaptoethanol.

EXAMPLE 10 The reactor was similar to that of example 1, with theexception that the fractionating column was removed and the outlet fromthe reactor was connected directly to a cold trap. A mixture of 267 g.triethylene glycol diethylether containing 0.67 weight percent H SO, wascharged to the reactor. The temperature was raised to 142 C. and avacuum of mm. Hg was drawn on the system. A total of 300 g. ofmercaptoethanol was slowly added to the reactor while maintaining thespecified pressure and temperature. In the run 94 percent of themercaptoethanol reacted with a 89 percent yield of ethylene sulfide,based on the reacted thioalcohol.

EXAMPLE 1 l A 500 ml. round bottom flask was connected to the bottom ofa Vigeraux column having a water cooled reflux condenser. Product fromthe reflux condenser was collected in dry ice cooled receivers. Vacuumin the system was maintained by a vacuum pump connected to thereceivers. A pump was used for adding the mercapto propanol at a uniformrate to the 500 ml. round bottom flask.

Two hundred grams of a technical grade l-tetradecanol, and 3 grams ofconcentrated sulfuric acid were charged to the round bottom reactionflask. After heating to 145 C. and regulating the pressure at 70 mm. Hg,99.9 grams of l-mercapto-2propanol were pumped to the reactor at about0.8 mLImin. After all the mercapto alcohol was added the reaction wascontinued for about 15 minutes and the vacuum reduced to 22 mm. Hg toremove any remaining mercapto alcohol from the reactor.

There was collected 21 grams of a water layer and 70 grams of an oillayer in the receivers. Estimated yield of propylene sulfide based onconverted mercapto propanol was 90-95 percent.

The procedure described below was used for examples 12-14.

Solvent and acid are added to a round bottom flask agitated by amagnetic bar. A pump for continuously adding the mercaptoalcohol isconnected to a side arm of the flask. Connected to a second opening onthe flask is a short 8"Xl/2" Vigeraux column that is followed by a smallwater cooled condenser, vacuum cutter, and a graduated receiver. Thevapor exit from the vacuum cutter passes to a dry ice cooled trap andfrom there to a pressure regulator and vacuum pump. The reaction flaskalso is equipped with a thermowell. The temperature of the reactionflask is controlled by a thermocouple in this thermowell.

After heating the solvent-catalyst system to the desired temperature andevacuating the system to the selected pressure, the mercapto alcohol isslowly added by the pump to the reactor. Reaction product is collectedin the graduated receiver and in the trap. After all the mercaptoalcohol is added, the reaction is continued until no further overheadproduct is obtained.

EXAMPLE 12 To the 125 ml. reaction flask was charged 50 grams ofpolyethylene glycol 400 mol. wt. and 0.5 grams of H 80 10.3 grams of3-mercapto-2 --butanol were added to the reactor at 0.2 ml./min. Thereactor temperature and pressure were 145 C. and 50 mm. Hg,respectively.

2.2 grams were collected in the receiver and 7.4 grams in the cold trap.Gas liquid chromatography showed the oil in the cold trap to be largely2,3-epithiobutane. Estimated yield was about 90 percent on the convertedmaterial.

EXAMPLE 13 To a 125 ml. reactor containing 50 grams of polyethyleneglycol 400 mol. wt. and 0.5 grams of H 80 were charged 10.5 grams of2,3-dimercaptopropanol at l45 C. and mm. Hg pressure. Feed rate wasabout 0.2 ml./rnin. Collected in the receiver was 6.1 grams with 2.9grams collected in the trap. The overhead material was largely mercaptopropyl thiirane. Yields were estimated between 80 and 90 percent.

EXAMPLE 14 Fifty grams of polyethylene glycol 400 mol. wt. and 0.30grams of sulfuric acid were charged to a 125 ml. reactor and heated to145 C. under 5 mm. Hg pressure. 19.8 grams oflbutoxy-3-mercapto-2-propanol were added to the reactor at about 0.2ml./min. l 1.75 grams of product were collected in the graduatedreceiver and 4.0 grams were condensed in the dry ice trap. Estimatedyield of lbutoxy-Z,B-epithiopropane was 70 percent.

EXAMPLE 15 The equipment was similar to that used for examples 12-14except for the elimination of the Vigeraux column. A 250 ml. reactionflask was used. 100 grams of a triethylene glycol mono-butyl ether andhigher polyethylene glycol monobutyl ether solvent along with 2.5 gramsof ptoluene sulfonic acid, tech. grade, were charged to the reactor.After heating to 145 C. and evacuating to 70 mm. Hg, 50 ml. or 51.7grams of 2- mercapto-propanol were added at about 0.6 ml./min. 28.4grams of mercaptopropanol were unconverted in the distillate. 1 1.3grams of propylene sulfide were obtained in the distillate for a yieldof 60 percent, based on converted mercaptopropanol.

To show the effect of employing a diluent which is a nonsolvent for thecatalyst, the following runs were made in the apparatus used forexamples 7-9.

A mixture of 67 percent parafiinic petroleum oil and 33 percent KHSO,was placed in a Waring Blender to comminute the KHSO... After thoroughmixing and grinding of the solids, the mixture was placed in a 250 m1.reactor. The mixture was heated to 145 C. at 10 mm. Hg. Then2,3-dimercaptolpropanol feed was started. Less than 1 m1. of thedimercaptopropanol was added when an uncontrollable foaming occurred.The pressure increased to 35 mm. Hg. After the foaming subsided, thepressure was again reduced to 10 mm. and addition of thedimercaptopropanol was again attempted, with a recurrence of thefoaming.

In a second comparative run, 120 grams of a ground mixture of 33 percentKHSO and 67 percent diphenyloxide were added to the reactor. The mixturewas heated to 145 C. at 10-12 mm. Hg. Then 10.3 grams of2,3-dimercapto-propanol were added at a rate of 0.3 ml. per minute. Thematerial condensed in the receiver weighed 4.2 grams and consistedprimarily of unreacted dimercaptopropanol. The material in the trapweighed 4.5 grams and was largely mercaptopropyl thiirane. The yield ofthe latter was less than 50 percent.

We claim: 1. A method of preparing compounds of the structure l BF]!R(CH2)n C\ /CH R S wherein R represents hydrogen, halogen, alkyl,haloalkyl, cycloalkyl, alkenyl, alkyloxy, aryloxy, aryl, aralykyl,alkaryl, carboxy, thioalkyl, hydroxyl and thiol groups in which theorganic radical has up to 10 carbon atoms and R and R" each representshydrogen and alkyl groups of from one to about two carbon atoms and n isan integer from 0 to 2, comprising continuously adding at a pressure offrom 1 to 200 mm. Hg a mercaptoalcohol of the structure wherein X and Yeach represents OH and SH and when one of X and Y is OH the other is SH,to a mixture heated to from about 1 10 to 220 C, said mixture consistingessentially of a solution of an acidic dehydration catalyst selectedfrom the group of sulfuric acid, phosphoric acid, alcohol sulfates,alcohol sulfonates of two to 20 C atoms, phenyl sulfonic acid, ringalkylated or halogen substituted phenyl sulfonic acids in an organicsolvent for said catalyst and said mercaptoalcohol, said solvent havinga vapor pressure no greater than about 10 mm. Hg at 70 C, said catalystbeing substantially nonvolatile at said dehydration temperature andpressure, and continuously volatilizing said thiirane from the mixture.

2. The method of claim I in which the catalyst is H 3. The method ofclaim 1 in which the catalyst is an alkanol sulfate or a sulfate of apolyalkyleneglycol ether.

4. The method of claim 1 in which the solvent is a polymer of molecularweight 200-4,000 of at least one epoxide having two to four C atoms.

5. The method of claim 1 in which the solvent is selected from the classconsisting of monoand diethers of polyalkylene oxides having two to sixalkylene groups, each said alkylene group having two to four C atoms,and said ether group having one to four C. atoms.

6. The method of claim 1 in which the solvent is an alkanol of from12-20 C atoms.

7. The method of claim 1 in which the catalyst concentration ranges fromabout 0.002 to about 0.2 acid equivalents per parts by weight ofsolvent.

8. The method of claim 7 in which the catalyst is H 80 9 The method ofclaim 1 in which the catalyst is an alkanol sulfate having two to 20 Catoms.

10. The method of claim 1 in which the reaction pressure ranges from 1to 200 mm. Hg.

11. The method of claim 1 in which the mercaptoalcohol ismercaptoethanol and the thiirane is ethylene sulfide.

12. The method of claim 1 in which the mercaptoalcohol ismercaptopropanol and the thiirane is propylene sulfide.

13. The method of claim 1 in which the mercaptoalcohol isl-mercapto-Z-butanol and the thiirane is 1,2-epithiobutane.

14. The method of claim 1 in which the mercaptoalcohol is2,3-dimercaptol propanol and the thiirane is mercaptopropyl thiirane.

15. The method of claim 1 in which the mercaptoalcohol is1butoxy-3-mercapto-2-propanol and the thiirane isl-butoxy2,3-epithiopropane.

16. The method of claim 1 in which a mixture of mercaptoalcohols havingtwo to four C atoms is dehydrated to form a mixture of correspondingthiiranes.

2. The method of claim 1 in which the catalyst is H2SO4.
 3. The methodof claim 1 in which the catalyst is an alkanol sulfate or a sulfate of apolyalkyleneglycol ether.
 4. The method of claim 1 in which the solventis a polymer of molecular weight 200 - 4,000 of at least one epoxidehaving two to four C atoms.
 5. The method of claim 1 in which thesolvent is selected from the class consisting of mono- and diethers ofpolyalkylene oxides having two to six alkylene groups, each saidalkylene group having two to four C atoms, and said ether group havingone to four C. atoms.
 6. The method of claim 1 in which the solvent isan alkanol of from 12 - 20 C atoms.
 7. The method of claim 1 in whichthe catalyst concentration ranges from about 0.002 to about 0.2 acidequivalents per 100 parts by weight of solvent.
 8. The method of claim 7in which the catalyst is H2SO4.
 9. The method of claim 1 in which thecatalyst is an alkanol sulfate having two to 20 C atoms.
 10. The methodof claim 1 in which the reaction pressure ranges from 1 to 200 mm. Hg.11. The method of claim 1 in which the mercaptoalcohol ismercaptoethanol and the thiirane is ethylene sulfide.
 12. The method ofclaim 1 in which the mercaptoalcohol is mercaptopropanol and thethiirane is propylenE sulfide.
 13. The method of claim 1 in which themercaptoalcohol is 1-mercapto-2-butanol and the thiirane is1,2-epithiobutane.
 14. The method of claim 1 in which themercaptoalcohol is 2,3-dimercapto-1-propanol and the thiirane ismercaptopropyl thiirane.
 15. The method of claim 1 in which themercaptoalcohol is 1-butoxy-3-mercapto-2-propanol and the thiirane is1-butoxy-2,3-epithiopropane.
 16. The method of claim 1 in which amixture of mercaptoalcohols having two to four C atoms is dehydrated toform a mixture of corresponding thiiranes.